Laserfiche WebLink
WATERSHED RESTORATION <br />with ahigh-resilience capacity are improving or have been <br />restored should restoration efforts focus on areas that have <br />generally lost the capability of natural recovery, even after <br />the cessation of human perturbations. However, special <br />situations may exist in which degraded habitats of species <br />near extinction can only be restored at high risk and cost; <br />such areas assume a high priority for improvement. <br />Where possible, managers should emphasize preservation <br />because preservation of intact ecosystems is typically less <br />expensive than restoring degraded systems (Cairns 1993). <br />Intact ecosystems are not only valuable sources of biologi- <br />cal diversity, but they also provide important reference <br />sites that land managers may seek to emulate in their <br />restoration activities. Rather than referring to a handbook, <br />]and managers should obtain the "blueprints" for the ulti- <br />mate outcomes of planned restoration activities in adjacent <br />sites from intact streams. Because the failure rate of restor- <br />ing degraded ecosystems is far greater than that of simply <br />protecting fully functional sites, protecting and preserving <br />intact ecosystems should represent the first priority of any <br />watershed-scale restoration plan. <br />At the other extreme, many areas exist where ecological <br />restoration in the strictest sense is neither economically, <br />socially, nor technologically feasible (e.g., metropolitan <br />__ <br />..Reviews of ~instream habitat -- <br />management-projects throughout the <br />western United States clearly indicate <br />that passive restoration has been <br />the critical first step in successful <br />riparian restoration` programs. <br />reaches, dredged mine sites, etc.). If restoration practices <br />are pursued in these situations, they may be costly. How- <br />ever, stream enhancement activities should not be ruled <br />out in these scenarios, particularly if such acti~-ities would <br />diminish harm to dot~-nstream or upstream riparian and <br />aquatic ecosystems. <br />Thy domain of riparian and stream restoration lies <br />bet~~•een these t~-~ o extremes (Figure 2). A successftl ri~ari- <br />-._~. restoraro. program ~~~ill result in the pemetuation of <br />`~~Ces~cs t;',at c'ietermine eCO~ysteil strLICLLlrv', illnCtlOn, <br />and eyoiutionar~~ trajector,~. Ho;~ e~.~er, this operating prin- <br />ciple is stated ~~•ith the recognition that the intact ~~-i1d- <br />lands of today and the future will exist in a fragmented <br />landscape and will require specific preservation manage- <br />ment activities such as prescribed fires, suppression of <br />arson fires, control of biotic invasions, and maintenance of <br />natural hydrologic disturbance regimes. <br />After identifying those degraded sites where restoration <br />is deemed feasible, scientists must determine the causes of <br />degradation and the activities preventing recovery (Besch- <br />ta 1997). Also important is the identification of biotic <br />components of the ecosystem that have been extirpated <br />and the presence of biotic invaders that may prevent recoy- <br />er~-. I~~ addition to biotic considerations, c~(enri;~; must <br />Fps _ ~-~ <br />determine the degree to which the hydrologic and geo- <br />morphic features of the ecosystem have been (or are being <br />altered. This includes determining the influences of past <br />management activities on channel morphology, channel <br />incision, hyporheic flows, water table dynamics, and Ovate <br />quality (i.e., the linkages between the terrestrial and aquat- <br />ic system). From this initial analysis, not only can the ex- <br />tent and causes of ecosystem degradation be addressed, brit <br />potential restoration options may become evident. Obviously, <br />even at this stage, restoration is a multidisciplinary effort. <br />The desired endpoints of restoration efforts are naturally <br />dynamic and self-sustaining ecosystems (Figure 2). Given <br />the fluctuating nature of environmental factors inherent to <br />all natural systems, restoration managers should empha- <br />size ecosystem processes and function rather than some <br />preconceived landscape form. Fisheries professionals should <br />recognize that because of the likely permanence of many <br />exotic species, extinctions of native species, long-term <br />changes in soil productivity due to erosion, and other severe <br />environmental perturbations, complete recovery may not <br />always be possible. In such cases, goals of restoration are <br />to return a riparian system to a "potential natural commu- <br />nity;" whereby the ecosystem is nahirally functioning in a <br />manner as closely as possible to that in which it evolved. <br />Passive Restora#ioti <br />Once professionals have decided where to implement <br />restoration activities, the first and most critical step is to <br />halt activities causing degradation or preventing recovery, <br />an approach referred to as yassiz~e or natural restoration <br />(Kauffman et al. 1993; Kauffman et al. 1995). Many ripari- <br />an zones are capable of rapid recovery after human per- <br />turbations stop because the biota has evolved adaptations <br />to survive and even reproduce despite frequent natural <br />disturbance events characteristic of riverine systems <br />(Barnes 1953; <'Nilson 1970; Gecy and Wilson 1990). <br />In western riparian zones the taco most common exam <br />pies of successful passive ecological restoration-are the <br />rewatering of streams after years of ~rithdrawal for a~ri- <br />cultural or municipal purposes and the cessation of li~-e- <br />stock grazing in riparian areas. Stream fio~~• diyersirn~., <br />combined ~+,•itii hea~-y li~-estock gazing, can resu1~ in serer, <br />degradation of riparian and stream ecosystems. ~~it~ the <br />return of perennial instream tio~~-s and the halt of li~~esto; b. <br />,razing, the recovery of riparian vegetation can be dra- <br />matic. For example, in the ;Mono basin of California, 215 <br />of the area of riparian vegetation lost during a 50-vr peri- <br />od of water diversion (1910-1989) had reestablished after <br />only 4 years following rewatering (Jones and Stokes Asso- <br />ciates, Inc., and Trihey Associates, persona] communica- <br />tion). Along these recovering streams, willow and cotton- <br />wood seedling densities were often >50 m'- with annual <br />growth rates of 0.6 to 1S m high (B. Kauffman and P.. Besch- <br />ta, Oregon State University, personal communication). <br />i~o~~; vegetation establishment is beginning to intiuence <br />channel diversity through the creation of narrower chan- <br />nels, bank undercuts, and pools. In contrast, while sec-er.: <br />million dollar; has been spe~;t or. en,ineern manipt;_ati~~~-.- <br />S~~c;a! Iss.e o~, ti~`~iefersned Restora_tio~ <br />